Field of the Invention
The present invention relates to a process for preparing a vinyl chloride resin composition whose surface gloss features are excellent and which has excellent transparency, weather resistance, and impact resistance.
As a means of improving the weather resistance as well as the impact strength of certain resins, it has been proposed to modify such resins with a crosslinked acrylic ester as an elastomer component. Moreover, in order to further improve the impact strength characteristics of the resin, it has been proposed to use an elastomer which has a double layer structure with an outer shell of an acrylic ester and an inner core of a polymer having a high glass transition temperature. Resins are known which are obtained by the graft polymerization of vinyl chloride, styrene, methyl methacrylate, or acrylonitrile in the presence of the above cross-linked double layer acrylic ester elastomer. However, the transparency of the vinyl chloride resin component (hereinafter referred to as PVC) of the compositions is diminished, although the compositions possess improved weather resistance and impact resistance. In order to improve the transparency and impact strength of PVC compositions, U.S. Pat. No. 3,763,279 discloses a resin in which vinyl chloride is graft-polymerized onto a cross-linked double layer elastomer having an outer shell of an acrylic ester and a styrene core. In order that the resulting composition possess excellent transparency, however, it is necessary to limit the acrylic ester content of the double layer elastomer to 44 to 48% by weight, but this amount is insufficient to fully develop the impact strength of the product. Moreover, it is difficult to obtain a vinyl chloride resin composition which possesses excellent surface gloss from such a double layer elastomer composition.
U.S. Pat. No. 3,971,835 discloses a graft copolymer for the modification of vinyl halide polymers which is produced by graft-polymerizing methyl methacrylate onto a crosslinked double layer elastomer having an outer layer of an acrylic ester and a styrene core. The resulting composition does not possess a fully developed impact strength, transparency and surface gloss.
U.S. application Ser. No. 644,421 discloses vinyl halide polymer compositions which contain a graft copolymer of a cross-linked double-layer elastomer where the graft copolymer is produced by first polymerizing methyl methacrylate in the presence of a rubber polymer latex followed by polymerization of styrene so that the resulting composition may possess excellent transparency, excellent surface gloss properties, improved weather resistance and impact resistance. However, the composition does not possess satisfactory thermal stability and the improvement in impact strength is unsatisfactory.
A need therefore, continues to exist for a vinyl chloride resin composition of improved thermal stability, transparency and surface gloss characteristics.